Departamento de Parasitología, Facultad de Medicina Veterinaria y Zootecnia, Universidad Autónoma de Yucatán, Yucatán, Mexico.
Vet Parasitol. 2010 Feb 26;168(1-2):165-9. doi: 10.1016/j.vetpar.2009.10.021. Epub 2009 Nov 4.
Three cattle farms with ticks, Rhipicephalus microplus, thought to be resistant to ivermectin in Yucatan, Mexico were studied (SFDO, SPN, LUADY). Each field-population was collected and tested twice several months apart. The larval immersion test was used on the progeny of collected adult females to test the susceptibility to ivermectin. Dose-mortality regressions, lethal concentrations (LC), their confidence intervals and slope were estimated by probit analysis. Resistance ratios (RR) were determined in the three investigated populations at the LC(50) and LC(99) estimates. The LUADY (RR(50): 2.04 and 2.29, RR(99): 2.67 and 3.55), SPN (RR(50): 3.55 and 3.68, RR(99): 8.19-11.06) and SFDO (RR(50): 6.84 and 8.59, RR(99): 54.17 and 87.86) ticks had significantly higher LC(50)/LC(99) than the reference susceptible Deutch strain, demonstrating resistance in the field-collected populations. Furthermore, there was significant difference between LC(50)/LC(99) of the SFDO, SPN and LUADY tick populations, which indicates not only the presence of resistant populations, but also different levels of resistance to ivermectin in the field populations studied. There was no difference observed at the LC(50) nor LC(99) estimates at two different times of collection from any of the three populations studied. In conclusion, we report for the first time field populations of R. microplus resistant to ivermectin in Mexico.
三个被认为对墨西哥尤卡坦伊维菌素具有抗药性的有蜱牛场（SFDO、SPN、LUADY）进行了研究。每个田间种群都被收集并在相隔数月的时间里进行了两次测试。幼虫浸浴试验用于测试收集的成年雌蜱后代对伊维菌素的敏感性。通过概率分析估计致死浓度（LC）、置信区间和斜率的剂量死亡率回归、致死浓度（LC）及其 50%和 99%置信区间的抗性比值（RR）。在三个被调查的种群中，在 LC（50）和 LC（99）估计值处确定了抗性比值（RR）。LUADY（RR（50）：2.04 和 2.29，RR（99）：2.67 和 3.55）、SPN（RR（50）：3.55 和 3.68，RR（99）：8.19-11.06）和 SFDO（RR（50）：6.84 和 8.59，RR（99）：54.17 和 87.86）蜱的 LC（50）/LC（99）显著高于参考敏感的 Deutch 株，表明田间采集的种群具有抗性。此外，SFDO、SPN 和 LUADY 蜱种群的 LC（50）/LC（99）之间存在显著差异，这不仅表明存在抗性种群，而且表明在研究的田间种群中对伊维菌素的抗性水平不同。在三个研究种群的任何一个种群的两次不同采集时间的 LC（50）或 LC（99）估计值都没有观察到差异。总之，我们首次报道了墨西哥对伊维菌素具有抗药性的 R. microplus 田间种群。
